Alien grasses that promote fire invaded the submontane seasonal zone of Hawai'i Volcanoes National Park starting in the 1960s. These grasses recover rapidly from fire, maintain a high dead-to-live biomass ratio, and burn at high relative humidities. Since 1970, the invasion of fire-promoting grasses has increased fire frequency 10-fold and fire size over 1000-fold. We monitored plant cover and density after 11 fires in 16 sites throughout the range of the submontane seasonal zone. These fires occurred between 1972 and 1992, and were sampled 1-21 years after fire. Fire significantly reduced native vegetation, almost entirely represented in the submontane seasonal zone by native trees and shrubs. The monodominant tree species, 'ohi'a (Metrosideros polymorpha), did not regenerate from seed in any burn. Fire killed on average 46% of 'ohi'a, markedly thinning forests and woodlands. Native shrub cover declined 17-fold, with the near loss of the formerly dominant shrub pukiawe (Styphelia tameiameiae) from most burns. The fire tolerant native shrub 'a'ali'i (Dodonaea viscosa) persisted in molasses grass sites and appeared to be capable of recovering to its former dominance in burns in which it was especially abundant prior to fire and molasses grass was absent. The loss of native trees and shrubs was greater in burns affected by high intensity fire. Alien grass cover and biomass increased in almost all burns, particularly where molasses grass (Melinis minutiflora) was present prior to fire. Fire enhanced the establishment of the aggressive alien invader faya tree (Myrica faya), especially in shrublands. The current park policy of suppressing all fires should be maintained because of the deleterious effects of fire on native plant communities. Research underway to revegetate fire damaged sites using mamane (Sophora chrysophylla), 'a'ali'i, and other fire-tolerant native plants should be expanded.

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